When a base station apparatus is installed in a mobile communication system, it is required to adequately set transmission power and a beam direction of the base station apparatus so as not to form a spot area where a mobile station (user equipment terminal) cannot communicate with any base station apparatus. Further, it is also required to reduce radio interference and the like from a neighboring cell so as to ensure communication quality in each coverage area of the base station apparatus. In ideal environments where there are no buildings and plural base stations are regularly distributed, the shape of the coverage areas is almost regular hexagonal. Further, when a base station is installed in the center of the coverage area having the regular hexagonal, the highest communication quality in the coverage area is obtained. However, in actual environments, there may be buildings or the like and the base station may be installed in limited area. As a result, the shape of the coverage area and the communication quality in the coverage area may not be ideal. To overcome the problem, when the coverage area is determined (i.e., in a coverage area design process), it is required to sufficiently determine radio propagation characteristics around the base stations and estimate the interference levels when the directivity pattern of the base station apparatus is changed to adjust (determine) the directivity pattern of the base station apparatus. Because of this feature, a person who carries out the above procedure is required to have highly technical knowledge in this field and further, the work burden of the person is far from trivial.
As a method to overcome the problem, there has been proposed a mobile communication system having a function of collecting distribution information of the neighboring base stations and mobile stations (user equipment (UE) terminals). In this system, based on the collected distribution information, the coverage area is automatically formed (see, for example, Patent Document 1). According to this technique (method), upon or after the installation of a base station, the base station acquires (receives) information from mobile stations located around the base station, the acquired (received) information including a received signal level received by each of the mobile stations, information of the base stations communicating with the mobile stations, and information of the total transmission power transmitted from the neighboring base stations. Based on the acquired information, the base station automatically determines the transmission power of the signal to be periodically broadcasted generally used for forming the coverage area of the base station without any assistance from an operator. By using this method, it may become possible for the base station to automatically form the coverage area in the mobile communication system by autonomically determining the transmission power of the broadcast signal of the base station while cooperating with the neighboring base stations.
Further, as the method of automatically forming the coverage area of the base station, there has been proposed a method of controlling the antenna directivity of the base station (see, for example, Patent Document 2). In this method, based on the information received from the mobile stations located around the base station, the information including the received signal level received by the mobile stations and based on the service coverage area information such as the traffic status of the base station and the neighboring base stations, the vertical plane directivity of the antenna of the base station is controlled. In the directivity control method, the antenna of the base station includes plural antenna elements aligned in a straight line in the vertical direction. By applying and cutting the signal to each of the antenna elements and by changing the phase of the signal applied to the antenna elements, and based on the service coverage area information, the number of antenna elements and the phases to be applied to the antenna elements are adjusted (controlled). By doing this, the antenna beam-width, antenna gain, and beam-tilt angle in the vertical plane of the directivity of the antenna are controlled. According to this method, it may become possible to flexibly form the coverage area of the base station based on the transmission power alone.    Patent Document 1: Japanese Patent Application Publication No.: 2006-135673    Patent Document 2: Japanese Patent Application Publication No.: 2005-109690